Mysteries of the Deep: Faulting in the offshore California Continental Borderlands

Jillian M. Maloney

Published August 15, 2019, SCEC Contribution #9808, 2019 SCEC Annual Meeting Talk on Wed 0830 (PDF)

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Despite recent seismic activity and decades of geophysical mapping, there is still much to learn about the offshore faults of the California Continental Borderlands. Namely, fault geometry, slip rates, and paleoseismic records are poorly constrained. Although lower slip rates (1-2 mm/yr) are estimated for most offshore faults, their potential hazard to southern California, where much of the population lives in coastal regions, should not be overlooked. In addition to direct hazard from seismic shaking, coastal areas can be prone to liquefaction, and offshore faulting has the potential to generate tsunami from either dip slip movement or triggering of submarine landslides. Given the complex nature of faulting in the region, one of the major unresolved questions is: how continuous is slip across multiple strands? For example, recent mapping and modeling have shown that the major coastal fault in the region, the Newport-Inglewood - Rose Canyon fault zone, has the potential to produce a M7.3 earthquake if it ruptures along the entire offshore length from San Diego to Los Angeles. Other onshore paleoseismic data suggests a cascading series of earthquakes from south to north along the fault system. However, there exist no paleoseismic data for the offshore fault segments to test these hypotheses. There are many difficulties associated with offshore fault studies, including a lack of outcrop and trenching scale studies and a limited seismic network. Even with these difficulties, an investment in research on California Continental Borderlands fault systems could greatly improve hazard assessments for the region, especially by constraining fault geometry and connectivity. Furthermore, although the majority of the motion between the Pacific and North American plates is accommodated on faults to the east, a better understanding of offshore faults would provide a more complete picture of the mechanics, geometry, and evolution of the plate boundary. This talk will highlight the significance of the Borderlands for fault hazard assessment in southern California.

Key Words
offshore faults, marine geohazards, California Continental Borderlands

Maloney, J. M. (2019, 08). Mysteries of the Deep: Faulting in the offshore California Continental Borderlands. Oral Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology